The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Engines produce particulate matter (PM) that is filtered from exhaust gas by a PM filter. The PM filter is disposed in an exhaust system of the engine. The PM filter reduces emission of PM that is generated during combustion. Over time, the PM filter becomes full. During regeneration, the PM may be burned within the PM filter. Regeneration may involve heating the PM filter to a combustion temperature of the PM. There are various ways to perform regeneration including modifying engine management, using a fuel burner, using a catalytic oxidizer to increase the exhaust temperature with after injection of fuel, using resistive heating coils, and/or using microwave energy.
As one example, an exhaust system may include a three-way catalyst converter (TWC), an oxidation catalyst (OC) and a particulate matter (PM) filter located downstream from an engine. Exhaust gas from the engine passes through the TWC, followed by the OC and then is filtered by the PM filter. The TWC reduces nitrogen oxides NOx, oxidizes carbon monoxide (CO) and oxidizes unburnt hydrocarbons (HC) and volatile organic compounds. The OC oxides CO remaining in the exhaust received from the TWC.
Continuing from the above example, spark of the engine may be retarded to heat up the engine and thus the exhaust system to initiate regeneration of the PM filter. As a result a large mass is heated including the engine, the TWC, the OC and the PM filter. The mass may be heated to a PM combustion temperature of, for example, 600-750° C. The increased temperatures of exhaust system components can decrease the operating life of the TWC and/or the OC. Also, an increased amount of fuel is required to provide this heating.